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+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+// This file is loaded into the browser window scope.
+/* eslint-env mozilla/browser-window */
+
+/**
+ * Utility functions for UI accessibility.
+ */
+
+var A11yUtils = {
+ /**
+ * Announce a message to the user.
+ * This should only be used when something happens that is important to the
+ * user and will be noticed visually, but is not related to the focused
+ * control and is not a pop-up such as a doorhanger.
+ * For example, this could be used to indicate that Reader View is available
+ * or that Firefox is making a recommendation via the toolbar.
+ * This must be used with caution, as it can create unwanted verbosity and
+ * can thus hinder rather than help users if used incorrectly.
+ * Please only use this after consultation with the Mozilla accessibility
+ * team.
+ * @param {string} [options.id] The Fluent id of the message to announce. The
+ * ftl file must already be included in browser.xhtml. This must be
+ * specified unless a raw message is specified instead.
+ * @param {object} [options.args] Arguments for the Fluent message.
+ * @param {string} [options.raw] The raw, already localized message to
+ * announce. You should generally prefer a Fluent id instead, but in
+ * rare cases, this might not be feasible.
+ * @param {Element} [options.source] The element with which the announcement
+ * is associated. This should generally be something the user can
+ * interact with to respond to the announcement. For example, for an
+ * announcement indicating that Reader View is available, this should
+ * be the Reader View button on the toolbar.
+ */
+ async announce({ id = null, args = {}, raw = null, source = document } = {}) {
+ if ((!id && !raw) || (id && raw)) {
+ throw new Error("One of raw or id must be specified.");
+ }
+
+ // Cancel a previous pending call if any.
+ if (this._cancelAnnounce) {
+ this._cancelAnnounce();
+ this._cancelAnnounce = null;
+ }
+
+ let message;
+ if (id) {
+ let cancel = false;
+ this._cancelAnnounce = () => (cancel = true);
+ message = await document.l10n.formatValue(id, args);
+ if (cancel) {
+ // announce() was called again while we were waiting for translation.
+ return;
+ }
+ // No more async operations from this point.
+ this._cancelAnnounce = null;
+ } else {
+ // We run fully synchronously if a raw message is provided.
+ message = raw;
+ }
+
+ // For now, we don't use source, but it might be useful in future.
+ // For example, we might use it when we support announcement events on
+ // more platforms or it could be used to have a keyboard shortcut which
+ // focuses the last element to announce a message.
+ let live = document.getElementById("a11y-announcement");
+ // We use role="alert" because JAWS doesn't support aria-live in browser
+ // chrome.
+ // Gecko a11y needs an insertion to trigger an alert event. This is why
+ // we can't just use aria-label on the alert.
+ if (live.firstChild) {
+ live.firstChild.remove();
+ }
+ let label = document.createElement("label");
+ label.setAttribute("aria-label", message);
+ live.appendChild(label);
+ },
+};